Boring tools of that kind are used for the inside turning of bores or concavely curved surfaces on workpieces, with a diameter of about 200 mm to 1 m and more. In a known tool of the kind set forth above, the mounting body substantially comprises a transverse member which is provided at both ends, at the end face thereof, with guides of square or rectangular cross-section which extend radially with respect to the axis of rotation of the transverse member. The shank of a respective tool head is radially displaceably guided in each of the guides, the shanks also being of square or rectangular cross-section. A respective fitting pin which is let into the transverse member engages into a respective one of three fitting bores which are provided in the shank of the tool head and which are disposed at a spacing from each other in the radial direction. Each tool head can be adjusted stepwise relative to the transverse member by means of the fitting bores and the fitting pin. The fitting pin thus forms an abutment surface which fixes the tool head relative to the mounting body in the radial direction. The tool head itself is releasably connected to the transverse member by means of a plurality of screws. After the tool head has been adjusted in a stepwise manner by means of the fitting pin and the fitting bores, setting of the desired machining diameter is effected by the cutting bit carrier being displaced in the radial direction with respect to the tool head. That known boring tool is comparatively expensive to produce, because of its guides of square or rectangular cross-section. Furthermore, the range of diameters which can be machined with one and the same transverse member is comparatively small. Thus one transverse member is suitable for example for machining diameters which are between 355 and 520 mm. Another transverse member is required for the range of diameters from 520 to 685 mm.
The invention is based on the problem of providing a boring tool of the kind set forth in the opening part of this specification, which permits machining over the maximum possible range of diameters, while being simple to produce and particularly stable. The invention further seeks to provide that precise presetting of the working diameter is also possible, using simple measuring equipment.
The invention provides that the mounting body which is of a hub-like configuration is provided at locations which are diametrally oppositely disposed with respect to its axis of rotation with a respective mounting bore with its axis extending radially with respect to the axis of rotation, the bore being surrounded by an abutment surface extending perpendicularly to the axis of the mounting bore, and that the tool head is provided with a fitting spigot which fits into the mounting bore and which is concentrically surrounded by an annular surface extending perpendicularly with respect to the axis of the fitting spigot, and with at least one respective intermediate portion which can optionally be fitted between the mounting body and the tool head and whose one end has a mounting bore with radial abutment surface, corresponding to the mounting bore in the mounting bore, and whose other end has a fitting spigot with an annular surface, corresponding to the fitting spigot of the tool head.
The mounting bores of the mounting body and the fitting spigots of the tool head are comparatively simple to produce. The range of diameters in respect of which one and the same mounting body can be used is comparatively large by virtue of using one or possibly a plurality of intermediate portions. Thus for example a single mounting body can be used for a range of diameters of from 398 to 762 mm, while only one further mounting body is required for the next range of diameters of from 698 to 1342 mm. The intermediate portions used may also be extension portions as are conventionally employed in system boring tools (for example the Komet-ABS-attachment tools with plug-in connection). In addition, the same intermediate portions can also be used in connection with mounting bodies which are intended for another range of diameters. The novel boring tool is also distinguished by a considerable degree of stiffness so that it is possible to operate with comparatively high forward feed rates. In addition, the tool gives a high degree of accuracy in regard to change. That provides that the cutting edge can be accurately preset on the tool head, outside the machine, on a presetting apparatus, using comparatively simple measuring equipment. That operation does not require any large measuring tool which corresponds to the respective large working diameter. When the tool head with the preset cutting edge on the mounting body is re-connected to the mounting body directly or by way of the interposition of an intermediate portion, the precise length of which is known, and that can be done with a small number of manual operations, then the boring tool is already of the desired machining diameter without any need for further measurement or setting of the tool on the machine itself. That substantially reduces the setting and preparation times on the machine.
An advantageous embodiment of the boring tool according to the invention provides that the mounting body has two further, diametrally oppositely disposed, radial mounting bores whose axes are each arranged in a displaced relationship through 90.degree. in the direction of rotation of the mounting body relative to the axes of the respective two first mounting bores, and that the abutment surfaces of the second mounting bores are at a different spacing from the axis of rotation from the abutment surfaces of the first mounting bores. That provides additional options in regard to variation of the machining diameter, depending on whether the tool heads are fitted into the first or the second mounting bores.
An advantageous embodiment in that respect provides that the spacings of the abutment surfaces of the mounting bores differ by an amount which is somewhat smaller than the maximum radial adjustment travel of the cutting bit carrier on the tool head.